1. Field of the Invention
This invention relates to active materials for a non-aqueous electrolyte battery and to a non-aqueous electrolyte battery.
2. Description of the Related Art
Studies are now being vigorously made on a non-aqueous electrolyte battery which is designed to be charged and discharged through the movement of lithium ion between a negative electrode and a positive electrode for the purpose of using the battery as a high-energy density battery.
Non-aqueous electrolyte batteries in which an active material for the positive electrode is made of lithium transition metal composite oxides (transition metal is Co, Mn, Ni, etc.) and an active material for the negative electrode is made of carbonaceous materials, are already commercialized.
In recent years, there has been studied to employ, as an active material for the negative electrode of non-aqueous electrolyte battery, spinel-type lithium titanate composite oxides exhibiting higher Li-absorbing/desorbing potential (i.e., about 1.55 V vs Li/Li+) as compared with carbonaceous materials and having a crystal structure belonging to the Fd3-m space group. Since the spinel-type lithium titanate composite oxides are minimal in voluminal changes on the occasion of charging/discharging, they are excellent in charge/discharge cycle characteristics. Further, since there is no possibility in principle that lithium is separated out of the spinel-type lithium titanate composite oxides, the battery can be charged using a large current.
However, in the case of spinel-type lithium titanate, the Li-absorbing/desorbing reaction proceeds at a voltage of about 1.55 V, so that when a lithium transition metal composite oxide, for example, LiCoO2 is used as an active material for the positive electrode, the battery voltage would become 2.3 V. This electrical potential is therefore lower than the battery voltage of 3.8 V that can be derived from a lithium ion secondary battery which has a carbon negative electrode/LiCoO2 positive electrode and is widely commercialized, thus leading to the degradation of energy density.